JPH08330270A - Method of etching compound semiconductor substrate - Google Patents

Abstract

PURPOSE: To provide an etching method by which a uniform etching thickness can be obtained, when etching a compound semiconductor substrate, using wet etchant. CONSTITUTION: Etching is performed by performing the process of soaking a compound semiconductor substrate by fixing a compound semiconductor substrate in a container charged with etchant, or the like consisting of mixed liquid among sulfuric acid, hydrogen peroxide solution, and water, and tilting or sliding the container 4 thereby shifting the etchant 4, and the process of exposing it to atmosphere repeatedly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wet etching method for compound semiconductor substrates.

[0002]

2. Description of the Related Art In a gallium arsenide high power field effect transistor, heat generated during operation is dissipated to a heat radiator in contact with the back surface of a semiconductor chip. Therefore, the thickness of the semiconductor chip itself is usually reduced to about 100 μm. This thinning step is performed by wet etching using sulfuric acid, hydrogen peroxide solution, a mixed solution of water and the like.

The conventional thin film forming process is as shown in FIG.
In order to protect the surface of the compound semiconductor substrate 1 on which the high power field effect transistor is formed, the surface to be etched is exposed by adhering it to the support plate 3 with the chemical resistant wax 2. In this state, the exposed rear surface of the compound semiconductor substrate 1 is immersed in an etching solution 5 in which sulfuric acid, hydrogen peroxide solution and water mixed in a container 4 are mixed at a volume ratio of 3: 1: 1. Remove by etching. At this time, the etching liquid is heated to about 30 ° C. and etching is performed in a stationary state (FIG. 3B).

In such a conventional etching method, since the etching solution is kept stationary, the reaction heat generated by the chemical reaction between the compound semiconductor substrate and the etching solution causes non-uniform convection of the etching solution, and the etching solution There was unevenness in the substitution, and the etching thickness varied. Usually, when the compound semiconductor substrate 1 having a thickness of about 400 μm is etched to a thickness of about 100 μm, the thickness after etching varies within the range of ± 20 to 25% within the surface of the compound semiconductor substrate. When such etching is performed, variations in the thickness of the semiconductor chips occur, which causes defects in the assembly process, and variations in operating temperature during element operation, resulting in lower yield.

[0005]

In the conventional etching method, since etching is performed in a stationary state, variations in etching thickness occur. In order to solve the above problems, it is an object of the present invention to provide an etching method with which the etching thickness is uniform.

[0006]

In order to achieve the above object, the present invention provides a method of etching a compound semiconductor substrate using a wet etching solution, wherein the compound semiconductor substrate is placed in a container filled with the etching solution. The step of immersing the compound semiconductor substrate in the etching solution by moving the etching solution and the step of exposing the compound semiconductor substrate to the atmosphere are repeated.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIG. Similar to the conventional example shown in FIG. 3, a compound semiconductor substrate 1 adhered on a supporting plate by a chemical resistant wax to protect a semiconductor device such as a high power field effect transistor formed on the surface is fixed in a container 4. . In the container,
An etching solution 5 in which sulfuric acid, hydrogen peroxide solution, and water are mixed at a volume ratio of 3: 1: 1 is filled. Here, before starting the etching, the container is tilted so that the compound semiconductor substrate 1 does not come into contact with the etching solution 5 (FIG. 1).
A).

By tilting the container 4 to the opposite side, the compound semiconductor substrate 1 is dipped in the etching solution 5 to start etching (FIG. 1B). Then, the container is further tilted to the opposite side to expose the compound semiconductor substrate 1 to the atmosphere (FIG. 1C). By exposing to the atmosphere here, the etching solution 5 used for etching the compound semiconductor substrate 1 can be completely removed from the compound semiconductor substrate 1. Further, the etching solution moves to the side opposite to the side where the compound semiconductor substrate 1 is fixed in the container 4, whereby the etching solution is sufficiently stirred. The immersion and the exposure were performed at such a speed that the immersion and the exposure were repeated once per second. In addition, this speed is
It can be appropriately selected depending on the size of the compound semiconductor substrate, the size of the container, the amount of the etching solution, and the like.

The method of moving the container 4 and moving the etching solution 5 accordingly is not limited to the method shown in FIG. FIG. 2 shows a second embodiment. The method shown in FIG. 2 is a method of sliding the container 4 horizontally while keeping the container 4 horizontal, instead of tilting the container left and right. Also in this method, when the compound semiconductor substrate 1 is fixed in the container 4, the container 4 is tilted and the compound semiconductor substrate 1 is fixed (see FIG. 2).
A), the container should be returned horizontally and slid to the left and right. As shown in FIG. 2B, the container 4 is slid in the direction of the arrow to move the etching liquid 5 onto the compound semiconductor substrate 1. Next, in the direction of the arrow in FIG.
By sliding, the etching solution 5 can be moved from above the compound semiconductor substrate 1 to expose the compound semiconductor substrate 1 to the atmosphere. Even when such a method is adopted, the etching liquid 5 can be sufficiently stirred as in the first embodiment. Further, instead of sliding the container 4 to the left and right, it is possible to move the etching solution by tilting or sliding the container 4 while drawing a circular orbit or an elliptical orbit.
Further, the compound semiconductor substrate 1 does not need to be fixed in parallel to the bottom of the container 4, and it is possible to adopt a method of fixing vertically.

As a result of etching by the above method, the variation in etching thickness of ± 20 to 25% in the conventional method can be suppressed to within ± 5%. This is because the present invention is a compound semiconductor substrate 1
The etching solution 5 involved in the etching can be promptly removed, the etching solution can be sufficiently stirred, and since the etching is performed intermittently, the temperature rise of the etching solution can be suppressed, It is thought that this is because the speed does not increase partially.

[0011]

As described above, according to the etching method of the present invention, the variation in the etching thickness can be suppressed to 1/4 to 1/5 of the conventional one. Thereby, the thickness of the semiconductor chip can be formed uniformly,
When adopted in the manufacturing process of a gallium arsenide high power field effect transistor, it can be manufactured with a high yield.

[Brief description of drawings]

FIG. 1 is an explanatory diagram illustrating a first embodiment of the present invention.

FIG. 2 is an explanatory diagram illustrating a second embodiment of the present invention.

FIG. 3 is an explanatory diagram illustrating a conventional etching method.

[Explanation of symbols]

 1 Compound Semiconductor Substrate 2 Chemical Resistant Wax 3 Support Plate 4 Container 5 Etching Solution

Claims (1)

[Claims] 1. When a compound semiconductor substrate is etched using a wet etching solution, the compound semiconductor substrate is placed in a container filled with the etching solution, and the etching solution is moved to obtain the etching solution. A method for etching a compound semiconductor wafer, which comprises repeating the step of immersing the compound semiconductor substrate and the step of exposing the compound semiconductor substrate to the atmosphere.